Whether she is on the small screen, the big screen, or anywhere in between, Jennifer Aniston is a knockout! But how does the 43-year-old actress stay in such great shape? She credits a healthy lifestyle and yoga with instructor and friend Mandy Ingber. On Tuesday, both were seen attending a Self Magazine book party at Soho House in West Hollywood to celebrate Ingber's new book, "Yogalosophy: 28 Days to the Ultimate Body Makeover."

Aniston and Ingbar met about 22 years ago and have remained "fitness friends" ever since. In a recent interview, Aniston reflected on how the two have changed since they first new each other,

"We were a lot rounder, we ate terribly. We did that, and then we sort of grew up a little bit more and we got jobs."

But it was especially through Yoga that Ingber helped Aniston find confidence and feel comfortable with herself.

"That was always my 'ugh', my legs," Aniston explained. "That's why I credit [Mandy Ingber] for [them] -- with yoga."

Ingber also remarked on the transformations she's witnessed in Aniston over the duration of their friendship,

"It's hard to say is that yoga or is it as we get older we grow into ourselves, but I've seen her become so empowered, so grounded in herself, so comfortable in her own skin. I've definitely watched that process happen and unfold, and I'm grateful that I've gotten to be the observer of that."

Aniston practices yoga with Ingber at least three times a week. Ingber also helps other celebrity clients, such as Kate Beckinsale, Brooke Shields, and Helen Hunt, maintain healthy lifestyles and enviable figures. 

Although Aniston is dedicated to her healthy lifestyle, she is not a complete stickler and admits that every now or then she has a "Cheat Day."

"Cheat days for me are usually ... it's either Mexican food ... maybe Italian pasta, but I think you always have to do it in moderation."